Treatment of coal



Patented Juiy i, 19%.

i stats FREDERICK GLYN PRICE, OF LONDON, ENGLAND, 588163703. '10 MINERALS SEPARA- 'IION NOBTE AMERICAN CORPORATION, OF NEW YORK, N. Y.

TREATMENT 0! GOAL.

H0 Drawing.

or relating to the treatment of coal, par-' ticularly by the flotation process.

It has been found that the coal (i. e., bituminous coal) from many mines is not uniform or homogeneous but (in addition to gangue) contains different kinds of coal, and it may be desirable to separate these from one another.

Four coal constituents have been described as being commonly found in natural (bituminous) coal, namely Vitrain a very bright coal with a conchoidal fracture;

Clarain abright coal that breaks with a snare fracture or crystalline fracture;

itrain and clarain commonly'have an ash which approximates in composition to the original plant ash.

Durain (which is generally harder than the others) a dull coal. The ash is shaley, i. e., contains silicates of alumina, etc., and seems to have been derived from infiltration of mud;

Fusain, sometimes called mineral char coal, or mother-of-coal, looks like wood charcoal, i. e., it has a fibrous appearance and is comparatively soft and crumbly. In bulk fusain looks dull as charcoal does, although under the microscope it seems to be composed of glistening lustrous needles.

For various reasons it may be desirable to separate from one another different coal constituents. For example, it may be desirable to separate those constituents which will produce a satisfactory metallurgical coke from those constituents which tend to prevent the formation of good metallurgical coke. Again, in many cases, it is required to produce a coal with a minimum of ash content.

In the ordinary process of treating coal by froth-flotation it is found that the order of flotation of the coal constituents is affected by the nature of the coal surface and also by the size of the particles. For particles of uniform size, the bright coal tends to float more readily than the dull coal, but

Application filed April 27, 1922. Serial No. 557,018.

at the same time the more finely divided coal tends to float more readily than coarser coal, so that the separation of bright coal from dull coal may not be completel effective owmg particularly to the flotation of the more finely divided particles of dull coal.

It is already known that in the application of the flotation processto coal concentration the durain does not float so readily as the bright coal, but the present invention deals particularly with the problem of the separation of fusain. I

Fusain is very soft and friable, and when coal 1s crushed the fusain readily goes into the most finely divided portion and there fore has a tendency to float out of what is considered to be its normal order of flotation as determined by the surface properties. Fusain is always higher in ash than the bright coal with which it is associated.

So far as the production of a metallurgical coke is concerned, the difficulty encountered hitherto with flotation concentrates is that the finely divided fusain floats very' readily, and if, therefore, a coal or slack contains about 50% of a coking coal and a small percentage. say 5% of fusain, the froth concentrate, when subjected to coking, gives rise to patches of fusain in the resulting coke, which show themselves in the form of What are called smutty partings, which are really Weak places due to the presence of the fusain. v

One object of this invention is in the flotation treatment of such coals to hinder or altogether inhibit the flotation of fusain in addition to the other undesired constituents, such as gangue (if any), which in the ordinary process would not be floated.

According to this invention a process for the separation from one another of certain constituents of heterogeneous coal by flotation is characterised by the addition to the pulp of a small proportion of a protective colloid which inhibits the flotation of one coal constituent but not of another.

According to a specific form of this invention a process for the differential separation of the bright coal from the fusain in a mixture containing them consists in agitating and/or aerating the crushed coal in water to which has been added a small proportion of one or more froth-producing reagents, and to which has also been added a small proportion of a protective colloid, such as tannin, starch, albumen, or glue, so as to produce a froth with a high content of bright coal and a low content of fusaln, and separating the froth.

The protective colloids which can be used in carrying out this invention ma be carbo-hydrates (such as starch granu ose), tannic acid, gelatines (such as lue), albumens, or derivatives of carbo-hy rates (such as caramel or dextrine). These protective colloids, when added to a mobile pulp of crushed coal and water, have the effect of reducing the floatability of all the const tuents; indeed, if these reagents be added 1n sufiicient quantity to a coal-water pulp, the entire solid contents may be wetted and rendered unfloatable, but these rotective colloids afi'ord effective means 0 discriminating between one kind of coal and another in froth-flotation, that is to say they enable the fusain to be kept from floating, while the types of coal more readily amenable to froth-flotation are allowed to float, provided the additions be used in suitable proportions.

The following are particulars of various protective colloids which have been used with success: Starch is the colloid which is preferred for the process on account of the small quantity required and the ease of obtaining it. n

Starch has been tested in many varletles all of which have been found to be efficacious. The starches of rice, wheat, potato and maize, and the starch known as Lintners soluble starch all give excellent results. So also does tapioca. Maize flour gives good results either in hot or cold circuits, having been tried at 32 and again at 51 C.

Starch solutions for use in the process are conveniently made by working the starch into a thin paste with cold water and pouring it into boiling water with stirring and bolling for a short time. The time of boiling is of little consequence. The solution may conveniently contain about 2% of starch.

Effective results can be obtained with an alkaline solution of starch, prepared by pouring the paste made with cold water into a 2% solution of caustic soda. The

final solution should contain 2% of starch and 2% of NaOH.

The quantity of starch required depends on the quantity of fusain present but generally is not more than i lb. of starch per ton of coal.

Glue of all grades appears to' give satisfactory results. The following are) the trade names of kinds which have been tried: French pale; light French; Scotch ordinary; Scotch pale; Scotch best. The glue, of course, is added to the pulp in solution in such amount as is found by trial to yield rea ers the desired results. Good results have been obtained with -& lb. of glue per ton of coal.

Tannic acid has been used with success in the proportion of about 1 lb. per ton of coal. possible that substances containing tannic acid together with other constituents may prove useful. In order to determine the utility of a given substance it is necessary to perform a simple test as it is not impossible that certain unidentified constituents destroy the effects of tannic acid.

Albumen has been found to give good results. For example, egg albumen has been used in the proportion of a} lb. per ton of coal treated. Blood albumen is also satisfactory.

The following additional substances have been tried with success: gelatine: caseine in neutral solution; caseine in alkaline solution; animal glutin; agar-agar.

When using the protective colloids above indicated, ordinary frothing agents may be added to the pulp for the purpose of producing the froth, such for example as cresol. The addition of separate froth-producing agents may not always be necessary however.

The addition of the colloids appears permanently to, preclude the flotation of the fusain. Conse uently, in treating dirty coals from whic it is necessary to remove the ash and shale, a preliminary concentration to recover the coal free from ash may be desirable. Thereafter the coal is retreated with the addition of the colloid to separate the bright coal, leaving .the fusain The following are examples of the application of the present invention:

Emample I.

A sample of coal was taken from the Armadale main seam of the Redford coal mine in Scotland. Examination by the eye and through the microscope disclosed the presence of the four constituents above mentioned, and in fact it has been found that the raw coal does not yield a satisfactory metallurgical coke. lit does yield coke but one which is not hard or strong enough for blast furnaces and the like. The coal, crushed to pass th inch aperture (5 mesh T. M. M.), was mixed with four times its weight of water so as to make a mobile pulp. There was added to the pulp a quantity of cresol amounting to 1 lb. per ton of the original coal and a quantity of paraflin (kerosene) amounting to 1.6 lbs. per ton of coal. These reagents were for the purpose of producing the coal-bearing froth. There was also added to the pulp a quantity of starch solution equivalent to i lb. of starch per ton of coal treated. The pulp was subjected to agitation and aeration, as

Cutch failed in one test but it is inseam is customary in froth-flotation treatment, and the froth was removed in two stages. The concentrate quite obviously contained a preponderance of bright coal, and yielded a highly satisfactory metallurgical coke. while the tailings quite obviously contained a preponderance of the dull coal, and this material, although not capable of producing a metallurgical coke, wassuitable for makihg briquettes.

Example H.

A lar e scale test was carried out at Ashington from the Bedding and Redford mines, Scotland.

The coke produced directly from this dross is of an exceedingly friable character, and is useless for metallurgical purposes, owing to the fact that the dross containsa large percentage of fusain, as well as durain and carboniferous and barren shales. When the dross is cleaned by ordinary flotation, the fusian is included with the bright coal in the concentrates. The dross was therefore treated specially to recover the bright coal substantially free from fusian, durain carboniferous shale and barren shale. The dross contained 21.5% ash, 26.0% volatile matter, and 47.0% fixed carbon. 120 tons of the dross were treated by flotation, the reagents used being :(1) cresol used at the rate of 0.4 lb. per ton of dross, (2) paraflin (kerosene) oil used at the rate of 0.6 lb. per ton of dress, (3) starch used at the rate of 0.25 lb. per ton of dross. The concentrates weighed 80 tons and contained 6.2% ash, 26.6% volatile matter, and 53.2% carbon, and were substantially free from fusian. They were then coked at the Bedley Coke Ovens, Scotland, and an excellent metallurgical coke was produced.

Samples of the coke were tested, and it was found that the strength was very great. In one test the limiting crushing strength was 5260 lbs. per square inch.

The expression protective colloid in this specification is intended to include those substances which exercise the same physical actions in regard to suspended particles as are generally exercised by protective colloids, i. e., the expression 1s intended to include those substances (of which starch granulose, tannin, gelatine, and albumen are types) which tend to prevent the flocculation of coal particles in water. The proportions of protective colloids which can be effectively used vary considerably according to their nature, although the proportions used up to date have all been small.

The invention has been described in its application to the froth-flotation treatment of coal, but it will be understood that the invention may also be applied'to other forms of flotation treatment of crude coal.

olliery, Northumberland, on dross What I claim as my invention and desire to secure by Letters Patent is 1. A process for obtaining good coking coal from heterogeneous coal containing it, which consists in agitating a pulp of. the suitably ground coal to effect froth-flotation of good coking ingredients thereof in the presence of a protective colloid which inhibits the flotation of other normally flotable coal, and separating the froth.

2. A process for the separation of heterogeneous coal into diflerent carboniferous constituents irrespective of the relative size of the particles, which consists in agitating a pulp of suitably round heterogeneous coal to effect frothotation concentration thereof, separating the "froth concentrates, and agitating a pulp of the resulting concentrates in the resence of a rotective colloid which inhibits flotation 0 one carboniferous constituent but not of another, to pro-. duce a coal-bearing froth, and collecting the froth.

3. A process for the flotation of coal wherein suitably ground heterogeneous coal containing fusain is made into a pulp with water and subjected to a flotation operation in the presence of a protective colloid so as to inhibit the flotation of fusain but not to inhibit the flotation of another normally flotable carboniferous ingredient.

4. A process for the separation of heterogeneous coal containing fusain into different carboniferous constituents irrespective of the relative size of the particles, which consists in agitating a pulp of suitably ground heterogeneous coal to eflect froth-flotation concentration thereof, separating the froth concentrates, and agitating a pulp of the resulting concentrates in the presence of a protective colloid which inhibits flotation of the fusain but not of another carboniferous constituent, to produce a coal-bearing froth, and collectin the froth.

5. process for the separation from one another of certain constituents of heterogeneous coal by froth flotation wherein the coal is made into a pulp with water and subjected to froth flotation separation in the presence of a froth producmg reagent and of a protective colloid which inhibits flotation of fusain.

6. A process for the differential flotation of bright coal from fusain in a mixture containing them which consists in aerating the crushed coal in water to which has been added a small proportion of starch.

7. A process for the diiferential flotation of bright coal from fusain in a mixture containirig them which consists in agitating and aerating the crushed coal in water to which has been added a small proportion of Starch. z

8. A process for the diflerential flotation of bright coal from fusain in a mixture conaerating the crushed coal iii Water to which has been added a small proportion of sta-rch end of frdthing agent sons to separate the" bright coal in the froth. 9. A process for the difierential 'flotetion of bright coal from fusain in a mixture contai'ning them which consists in agitating and aerating the crushed coalin water to which has been added 91 small proportion Of starch, 10 not exceeding &% by weightbf'the coal, and of frothing agent so as to separate the bright coal in the froth.

In testimony whereof I affix my signature."

FREDERICK eL-Y PRICE. 

